The present invention relates to a coolant circulation system for a vehicle-mounted internal combustion engine.
Japanese Laid-Open Patent Publication No. 2008-169750 discloses a coolant circulation system that executes circulation stop control for stopping circulation of the coolant after the internal combustion engine starts up, for the purpose of promoting the warm-up of the internal combustion engine. This coolant circulation system changes the period during which the circulation stop control is executed in accordance with the temperature of the coolant detected at the start of the circulation stop control. Specifically, the lower the temperature of the coolant at the start of the circulation stop control, the greater becomes a determination value for terminating the circulation stop control. In addition, the circulation stop control is terminated based on the fact that the time during which the circulation stop control is executed or an accumulated air amount during the circulation stop control has reached a determination value.
The lower the temperature of the coolant at the start of the circulation stop control is, the longer becomes the time required for completing the warm-up. For this reason, the coolant circulation system sets a termination condition such that the lower the temperature of the coolant at the start of the circulation stop control is, the longer becomes the period during which the circulation stop control is executed.
An internal combustion engine is provided with a liquid temperature sensor for detecting the temperature of the coolant is provided. As described above, if the period during which the circulation stop control is executed is changed in accordance with the temperature of the coolant at the start of the circulation stop control, the coolant may boil in the part of the internal combustion engine with a higher temperature of the coolant than that in the vicinity of the liquid temperature sensor. Consequently, while the circulation stop control is executed in accordance with the temperature of the coolant at the start of the circulation stop control, the temperature of the coolant may reach the boiling point in the part of the internal combustion engine with a higher temperature of the coolant than that in the vicinity of the liquid temperature sensor.
For example, to prevent the coolant from boiling even when the temperature of the coolant in the internal combustion engine is not uniform, the determination value may be reduced. In this case, the circulation stop control terminates at a lower temperature. However, in such a case, the circulation stop control may be terminated before the warm-up is performed sufficiently. This may reduce, the effect of promoting the warm-up by the circulation stop control.